Method for estimating vehicular running state, vehicular running state estimating device, vehicle control device, and tire wheel

ABSTRACT

The output level (vibration level) of vibration of a portion below the spring of a vehicle detected by a vibration sensor mounted to the portion below the spring of the vehicle is frequency converted by frequency analyzing means  14 F to obtain the frequency spectrum of the vibration level and an operation is carried out on at least two vibration levels at different frequency bands of the obtained frequency spectrum by vibration level computing means  14 R, and this computed value is compared with a master curve showing the frequency spectrum of vibration level stored in vibration level storage means  16 S to estimate the condition of a road surface so as to estimate the running state of the vehicle.  
     Further, the running state of each tire including the air pressure of the tire is detected from the vibration level of the portion below the spring of the vehicle to estimate the running state of the vehicle, thereby constructing a multi-function sensing system for estimating the condition of a road surface or the running state of the tire with one sensor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus forestimating the running state of a vehicle by estimating the condition ofa road surface or the running state of each tire while running, anapparatus for controlling a vehicle based on the estimated running stateof a vehicle, and a tire wheel comprising the above vehicle runningstate estimation apparatus and a power generating unit for activatingthis apparatus.

[0003] 2. Description of the Prior Art

[0004] In recent years, it has been desired that the relationshipbetween each tire and the surface of a road which is the most importantfactor for the safe running of a vehicle, specifically, the groundcontact state of the tire typified by a friction coefficient between thetire and the surface of a road (road surface friction coefficient) orthe condition of a road surface, or the running state of the tire suchas the distortion and air pressure of the tire should be estimated withhigh accuracy and fedback to vehicle control. That is, if the aboveground contact state and running state of the tire can be estimated inadvance, before the operation of avoiding a risk such as braking orsteering is taken, high-level control of an ABS brake will be madepossible and further improvement of safety will be expected. The drivercan carry out deceleration operation earlier if he is informed of therisk of the condition of a road surface while running, whereby areduction in the number of accidents can be expected.

[0005] To estimate a road surface friction coefficient, there areproposed a method of estimating a road surface friction coefficientmaking use of the fact that the uniformity level of each tire which is aphysical quantity indicative of a change in the revolution speed of eachwheel is changed by the size of a road surface friction coefficient(Japanese Laid-open Patent Application No. 2000-55790) and a method ofestimating a road surface friction coefficient making use of the factthat the horizontal-direction vibration of each tire having a toe angleis detected by attaching an accelerometer to a lower arm for connectingthe front wheels and the vehicle body and this vibration level ischanged by a road surface friction coefficient (Japanese Laid-openPatent Application No. 6-258196) However, in the above method ofestimating a road surface friction coefficient from the uniformity levelof the tire, the uniformity is deteriorated by the formation of a flatspot in the tire and in the course of recovery from this, accurateestimation is difficult.

[0006] Meanwhile, in the above method of estimating a road surfacefriction coefficient from the horizontal-direction vibration of thefront wheels having a toe angle, the measurement accuracy is low whenthe slip angle of the tire is taken completely null or large.

[0007] There is also proposed a method of estimating a road surfacefriction coefficient from transmission characteristics betweenacceleration below a spring which is acceleration in the verticaldirection of each wheel and acceleration above the spring which isacceleration in the vertical direction of the vehicle body (JapaneseLaid-open Patent Application No. 11-94661). This method has such anadvantage that the road surface friction coefficient on a straight roadfor which almost no steering action is carried out can be estimatedbecause steering force is not used for the estimation of a road surfacefriction coefficient. However, as the road surface friction coefficientis estimated from vibration transmission characteristics between twopoints through a suspension unit having large buffer characteristicssuch as a spring or damper, the road surface friction coefficient isreadily affected by the uneven surface of the road. For instance, asvibration under a spring is large on a rough road such as a road coveredwith snow, the difference in vibration level between vibration above thespring absorbed by a suspension and vibration below the spring becomeslarge, thereby making it impossible to estimate a road surface frictioncoefficient accurately.

[0008] Meanwhile, the internal pressure of the tire is also an importantfactor for the running condition of the tire. Stated more specifically,the ground contact state of the tire and the running state of the tireare accurately estimated from the distortion state or vibration level ofthe tire while rolling and grip performance is improved or ridingcomfort is improved by increasing the ground contact area or rigidity ofthe tire is reduced to reduce the internal pressure of the tire when thegrip performance of the tire is reduced on a wet road or road coveredwith iced snow or when the vehicle runs on a rough road. Conversely whenthe vehicle runs at a high speed or a hydroplaning phenomenon occurs,the running fuel cost must be improved or the recovery of steerabilitymust be promoted by increasing the internal pressure of the tire.

[0009] However, since a sensor, which is ground contact state detectionmeans for measuring the distortion state or vibration level of the tirewhile rolling, requires a electric power source, the power must besupplied to the above sensor. Further, when an apparatus for estimatingor controlling the condition of a road surface or the running state ofthe tire based on the output of the above ground contact state detectionmeans and a radio unit for transmitting an output signal from roadsurface condition estimation means or the like to the vehicle body aremounted to the tire, a electric power supply to the above apparatus andradio unit is necessary.

[0010] For the power supply to the tire as a rotor, electromotive forceis transferred through a slip ring or generated by electromagneticinduction making use of relative movement between vehicle body and thetire may be used. However, the structure of the vehicle body must bechanged for means of supplying power to these, thus boosting costs.

[0011] Although it can be said that it is the most realistic method toload batteries which are to be exchanged, there remain such problems asthe troublesome exchange and service life of the batteries.

[0012] The development of a system which estimates the running state ofa vehicle such as the condition of a road surface or the running stateof each tire accurately, supplies information on the running state ofthe vehicle to the vehicle and the driver and controls thecharacteristics of the tire using the above information to provide amore safe or more comfortable running state has been desired.

[0013] It is an object of the present invention which has been made inview of the above problems of the prior art to provide a method andapparatus for estimating the running state of a vehicle such as thecondition of a road surface or the running state of each tire whilerunning accurately, a vehicle control apparatus for improving the safetyof a vehicle by feedback controlling the running state of the vehiclebased on the estimated condition of a road surface or the estimatedrunning state of each tire, and a tire wheel comprising the abovevehicle running state estimation apparatus and a power generating unitfor activating the apparatus.

SUMMARY OF THE INVENTION

[0014] To attain the above object, the inventor of the present inventionhas conducted various studies and has found that the running state of avehicle such as the condition of a road surface or the running state ofeach tire while running is estimated by detecting the vibration level ofa portion below the spring of a running vehicle or the vibrationtransmission level between at least two points of a portion below thespring of the vehicle, thereby making it possible to estimate therunning state of the vehicle accurately even when the road is rough,which has been difficult with the prior art, or when the slip angle isnull. The present invention has been accomplished based on this finding.

[0015] That is, according to a first aspect of the present invention,there is provided a vehicle running state estimation method comprisingthe steps of detecting the vibration level of a portion below the springof a running vehicle, and estimating at least one of the condition of aroad surface on which the vehicle is running and the running state ofeach tire based on the above detected vibration level to estimate therunning state of the vehicle. Generally the portion below the spring ofthe vehicle means a suspension, hub, brake caliper, wheel, and tire. Inthe case of having no spring in the suspension such as hydraulic unitthe portion means on the tire side from the unit.

[0016] According to a second aspect of the present invention, there isprovided a vehicle running state estimation method, wherein the waveformof time changes in the above vibration level is detected and thecondition of a road surface on which the vehicle is running is estimatedfrom a vibration level at a predetermined position of this waveform orfor a predetermined time range.

[0017] According to a third aspect of the present invention, there isprovided a vehicle running state estimation method, wherein thefrequency of the above detected vibration level is analyzed a vibrationlevel at a predetermined frequency band and the condition of a roadsurface on which the vehicle is running is estimated from the abovecalculated vibration level.

[0018] According to a fourth aspect of the present invention, there isprovided a vehicle running state estimation method, wherein thefrequency of the above detected vibration level is analyzed, at leasttwo vibration levels at different frequency bands are calculated, anoperation is carried out on the above calculated vibration levels, andthe condition of a road surface on which the vehicle is running isestimated from the operated value.

[0019] According to a fifth aspect of the present invention, there isprovided a vehicle running state estimation method, wherein thevibration levels of at least two points of a portion below the spring ofa running vehicle are detected to calculate the vibration transmissionlevel of the portion below the spring of the vehicle, and the conditionof a road surface on which the vehicle is running is estimated from theabove calculated vibration transmission level.

[0020] According to a sixth aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising:

[0021] means of detecting the vibration level of a portion below thespring of a running vehicle;

[0022] means of computing the waveform of time changes in the abovevibration level; and

[0023] road surface condition estimation means for estimating thecondition of a road surface on which the vehicle is running from avibration level at a predetermined position of the above waveform or fora predetermined time range.

[0024] According to a seventh aspect of the present invention, there isprovided a vehicle running state estimation apparatus which furthercomprises means of calculating the vibration level of at least one of atire leading edge portion, tire ground contact portion and tire trailingedge portion of the above waveform.

[0025] According to an eighth aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising:

[0026] means of detecting the vibration level of a portion below thespring of a running vehicle;

[0027] means of calculating a vibration level at a predeterminedfrequency band by analyzing the frequency of the above detectedvibration level; and

[0028] road surface condition estimation means for estimating thecondition of a road surface on which the vehicle is running from theabove calculated vibration level.

[0029] According to a ninth aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising:

[0030] means of detecting the vibration level of a portion below thespring of a running vehicle; and

[0031] road surface condition estimation means for estimating thecondition of a road surface on which the vehicle is running from a valueobtained by carrying out an operation on at least two vibration levelsat different frequency bands by analyzing the frequency of the abovedetected vibration level.

[0032] According to a tenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising:

[0033] means of detecting the vibration levels of at least two points ofa portion below the spring of a running vehicle;

[0034] means of calculating a vibration transmission level at apredetermined frequency band between the at least two of the abovevibration detection points; and

[0035] road surface condition estimation means for estimating thecondition of a road surface on which the vehicle is running from theabove calculated vibration transmission level.

[0036] According to an eleventh aspect of the present invention, thereis provided a vehicle running state estimation apparatus, wherein avibration buffer member is interposed between the above at least twovibration detection points.

[0037] According to a twelfth aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein therelationship between road surface friction coefficient μ obtained fromthe braking distances of a vehicle under various road conditions atdifferent speeds and the above vibration level at a predeterminedfrequency band, the computed value of vibration level or vibrationtransmission level is obtained previously and the road surface frictioncoefficient μ at the time of running is estimated based on the aboverelationship.

[0038] According to a thirteenth aspect of the present invention, thereis provided a vehicle running state estimation apparatus, wherein theabove frequency band is a band including the frequency of naturalvibration of a tire tread land portion.

[0039] According to a fourteenth aspect of the present invention, thereis provided a vehicle running state estimation apparatus, wherein athreshold value is set for the above vibration level and the surface ofa road is estimated to be in a low friction condition when thecalculated vibration level exceeds the above threshold value.

[0040] According to a fifteenth aspect of the present invention, thereis provided a vehicle running state estimation apparatus, wherein theabove threshold value can be changed.

[0041] According to a sixteenth aspect of the present invention, thereis provided a vehicle running state estimation apparatus which furthercomprises vehicle speed detection means to estimate the condition of aroad surface based on vehicle speed.

[0042] According to a seventeenth aspect of the present invention, thereis provided a vehicle running state estimation apparatus comprising thevehicle running state estimation apparatus of any one of claims 6 to 16,means of judging the slipperiness of a road surface based on thecondition of the road surface estimated by the road surface conditionestimation means of the vehicle running state estimation apparatus andwarning means for giving a warning when it is judged that the conditionof the road surface is slippery.

[0043] According to an eighteenth aspect of the present invention, thereis provided a vehicle running state estimation apparatus which furthercomprises vehicle speed detection means to change decision on theslipperiness of a road surface and warning level based on vehicle speed.

[0044] According to a nineteenth aspect of the present invention, thereis provided a vehicle running state estimation apparatus comprising:

[0045] means of detecting the vibration level of a portion below thespring of a running vehicle;

[0046] means of estimating the air pressure of each tire by calculatingthe frequency of natural vibration of the tire from a vibration level ata frequency band of 200 Hz or less of the above detected vibrationlevel; and

[0047] tire running state estimation means for estimating the conditionof each tire while running from the above estimated air pressure of thetire.

[0048] According to a twentieth aspect of the present invention, thereis provided a vehicle running state estimation apparatus which furthercomprises tire pressure monitoring means for monitoring the pressure ofeach tire while running using the above estimated air pressure of thetire.

[0049] According to a twenty-first aspect of the present invention,there is provided a vehicle running state estimation apparatus whichfurther comprises warning means for warning a passenger of a reductionin the pressure of the tire when the air pressure monitored by the abovetire pressure monitoring means falls below a predetermined value.

[0050] According to a twenty-second aspect of the present invention,there is provided a vehicle running state estimation apparatuscomprising:

[0051] means of detecting the vibration level of a portion below thespring of a running vehicle;

[0052] tire revolution speed detection means;

[0053] tire running state estimation means for estimating the state ofeach tire while running by calculating the average value of vibrationlevel changing by the revolution speed of the tire at a frequency bandof 100 Hz or less of the above detected vibration level; and

[0054] tire trouble detection means for judging that the tire isabnormal when the above calculated average value of vibration levelexceeds a preset reference value.

[0055] According to a twenty-third aspect of the present invention,there is provided a vehicle running state estimation apparatus, whereinthe above reference value is set to a range of 1.2 to 5 times thevibration level at a reference decision frequency Fn when the vehicleruns at a predetermined speed V while the tire is not abnormal:

reference decision frequency Fn=n×V/(2πr)

[0056] wherein r is the rolling radius of the tire, and n is 1, 2, 3, .. .

[0057] According to a twenty-fourth aspect of the present invention,there is provided a vehicle running state estimation apparatus, whereinthe above reference value can be changed.

[0058] According to a twenty-fifth aspect of the present invention,there is provided a vehicle running state estimation apparatus whichfurther comprises a transmitter for transmitting the output of the abovevibration detection means for calculating a time change in vibrationlevel or a vibration level at a predetermined frequency band.

[0059] According to a twenty-sixth aspect of the present invention,there is provided a vehicle running state estimation apparatus furthercomprising a electric power generating unit which is mounted to a tirewheel, generates power by the rolling of each tire and supplies powerfor driving the above vibration detection means or power for amplifyingthe output of the above vibration detection means.

[0060] According to a twenty-seventh aspect of the present invention,there is provided a vehicle control apparatus comprising vehicle controlmeans for controlling the running state of a vehicle based on thecondition of a road surface estimated by the vehicle running stateestimation apparatus of any one of claims 6 to 26 and/or the runningstate of each tire.

[0061] According to a twenty-eighth aspect of the present invention,there is provided a vehicle control apparatus which comprises vehiclespeed detection means to control the running state of a vehicle based onvehicle speed.

[0062] According to a twenty-ninth aspect of the present invention,there is provided a vehicle control apparatus for comprising means forcontrolling the locked state of each wheel such as ABS to control therunning state of a vehicle.

[0063] According to a thirtieth aspect of the present invention, thereis provided a vehicle control apparatus comprising means for controllingthe attitude of a vehicle to control the brake unit of each wheelindependently so as to control the running state of a vehicle.

[0064] According to a thirty-first aspect of the present invention,there is provided a vehicle control apparatus comprising means forcontrolling the air pressure of each tire to control the running stateof a vehicle.

[0065] According to a thirty-second aspect of the present invention,there is provided a vehicle control apparatus comprising means forcontrolling the idling state of each wheel by controlling a brake unitor engine speed.

[0066] According to a thirty-third aspect of the present invention,there is provided a vehicle control apparatus comprising means forchanging the inter-vehicle distance set value of an automatic drivingsystem based on the above estimated condition of a road surface so as toset an appropriate inter-vehicle distance.

[0067] According to a thirty-fourth aspect of the present invention,there is provided a tire wheel comprising the vehicle running stateestimation apparatus as set forth in any one of claims 6 to 26 and aelectric power generating unit for generating power by the rolling ofeach tire and supplying power to the above vehicle running stateestimation apparatus. Therefore, as the running state of the vehicle canbe estimated for a long time without changing the structure of thevehicle body, the running state of the vehicle can be controlled stably.

[0068] According to a thirty-fifth aspect of the present invention,there is provided a tire wheel, wherein the above vehicle running stateestimation apparatus is mounted to the tire wheel.

[0069] According to a thirty-sixth aspect of the present invention,there is provided a tire wheel, wherein the power generating unitcomprises a rotor magnetized and rotated by the rolling of each tire, astator made from a high magnetic permeability material and adjacent tothe rotor and a power generating coil installed within a magneticcircuit including the rotor and the stator. Therefore, power supply tothe above vehicle running state estimation apparatus is made possiblesemi-permanently and its functions can be retained for a long time.

[0070] According to a thirty-seventh aspect of the present invention,there is provided a tire wheel, wherein the power generating unitcomprises means of accumulating electromotive force generated in theabove power generating coil. Therefore, stable power supply is possibleregardless of the running state of the vehicle.

[0071] According to a thirty-eighth aspect of the present invention,there is provided a tire wheel, wherein the rotor is turned by rotatingan unbalance weight the gravity center of the rotary cone of which iseccentric to a rotary shaft by the rolling of each tire indirectly orthrough power transmission means.

[0072] According to a thirty-ninth aspect of the present invention,there is provided a tire wheel, wherein an air stream generated by therolling of each tire is introduced into the above power generating unitand the above rotor is turned by the above introduced air stream.

[0073] The other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0074]FIG. 1 is a diagram showing the constitution of a vehicle runningstate estimation apparatus according to Embodiment 1 of the presentinvention;

[0075] FIGS. 2(a), 2(b) and 2(c) are diagrams showing the installationlocations of vibration sensors according to Embodiment 1 of the presentinvention;

[0076]FIG. 3 is a diagram showing time changes in the vibration level ofeach tire according to Embodiment 1 of the present invention;

[0077] FIGS. 4(a) and 4(b) are diagrams showing vibration leveldistributions in the circumferential direction of the tire on a regularroad surface according to Embodiment 1 of the present invention;

[0078] FIGS. 5(a) and 5(b) are diagrams showing vibration leveldistributions in the circumferential direction of the tire on an icedroad according to Embodiment 1 of the present invention;

[0079]FIG. 6 is a diagram showing the constitution of a vehicle runningstate estimation apparatus according to Embodiment 2 of the presentinvention;

[0080] FIGS. 7(a) and 7(b) are diagrams showing the spectra of vibrationin the circumferential direction of the tire according to Embodiment 2of the present invention;

[0081]FIG. 8 is a diagram showing the constitution of a vehicle runningstate estimation apparatus according to Embodiment 3 of the presentinvention;

[0082]FIG. 9 is a diagram showing the relationship between the computedvalue of vibration level and vehicle speed under various road surfaceconditions according to Embodiment 3 of the present invention;

[0083]FIG. 10 is a diagram showing the constitution of a vehicle runningstate estimation apparatus according to Embodiment 4 of the presentinvention;

[0084]FIG. 11 is a diagram showing the installation locations ofvibration sensors according to Embodiment 4 of the present invention;

[0085] FIGS. 12(a) and 12(b) are diagrams showing the vibration spectraof vibration transmission level according to Embodiment 4 of the presentinvention;

[0086]FIG. 13 is a diagram showing another installation location of avibration sensor according to Embodiment 4 of the present invention;

[0087]FIG. 14 is a diagram showing the relationship between road surfacefriction coefficient μ and vibration transmission level according ofEmbodiment 4 of the present invention;

[0088]FIG. 15 is a diagram showing the constitution of a road slip alarmaccording to Embodiment 5 of the present invention;

[0089]FIG. 16 is a diagram showing a warning zone map according toEmbodiment 5 of the present invention;

[0090]FIG. 17 is a diagram showing the constitution of a roadslipperiness warning apparatus according to Embodiment 6 of the presentinvention;

[0091]FIG. 18 is a diagram showing a warning zone map according toEmbodiment 6 of the present invention;

[0092]FIG. 19 is a diagram showing the constitution of a vehicle runningstate estimation apparatus according to Embodiment 7 of the presentinvention;

[0093]FIG. 20 is a diagram showing the relationship between thefrequency of natural vibration and the air pressure of the tireaccording to Embodiment 7 of the present invention;

[0094]FIG. 21 is a diagram showing the constitution of a vehicle runningstate estimation apparatus according to Embodiment 8 of the presentinvention;

[0095]FIG. 22 is a diagram showing a detection example of a tirepeel-off trouble according to Embodiment 8 of the present invention; and

[0096]FIG. 23 is a diagram showing the constitution of a vehicle controlapparatus according to Embodiment 9 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0097] Preferred embodiments of the present invention will be describedhereinbelow with the reference to the accompanying drawings.

EMBODIMENT 1

[0098]FIG. 1 is a block diagram showing the constitution of a vehiclerunning state estimation apparatus 10 according to Embodiment 1 of thepresent invention. In the figure, reference numeral 11 denotes avibration sensor installed on the inner surface of a tire tread, 12vehicle speed detection means for detecting vehicle speed based on theoutput pulse of a revolution sensor 12 a for detecting the speed of awheel, 13 vibration waveform detection means for obtaining the waveformof vibration by arranging the output levels (vibration levels) of theabove vibration sensor in time sequence, 14 vibration level distributioncomputing means for obtaining the vibration level distribution of a tiretread by computing the vibration levels in a leading edge portion, aground contact portion and a trailing edge portion of the tire using theoutput pulses of the above revolution sensor 12 a, and 15 road surfacecondition estimation means for estimating the condition of a roadsurface which is one of the running states of a vehicle from the abovecomputed vibration level and the detected vehicle speed using thepreviously obtained master curve of vibration level depending on vehiclespeed stored in vibration level storage means 16.

[0099] In this Embodiment 1, the vibration sensor 11 for measuring thevibration state of a tire tread is installed on the inner surface 1A ofthe tire tread (to be simply referred to as “tread” hereinafter) asshown in FIG. 2(a) but the installation location of the vibration sensor11 is not limited to this. It may be installed on a portion below thespring of a vehicle, for example, the outer side of the rim 2A of a tirewheel portion 2 or the suspension arm 3A of a suspension portion 3 asshown in FIGS. 2(b) and 2(c).

[0100] The above master curve of vibration level is drawn by fixing thevibration sensor 11 on the inner surface 1A of the tread 1 of a testvehicle and causing the vehicle to run on road surfaces which differ inroad surface friction coefficient μ at a speed V to actually measure thevibration level of the above tread 1.

[0101] A description is subsequently given of the method of estimatingthe condition of a road surface.

[0102] First, the vibration level of the tread 1 while running isdetected by the vibration sensor 11 installed on the inner surface 1A ofthe tread 1, a vibration waveform formed by arranging the detectedvibration levels in time sequence is obtained by the vibration waveformdetection means 13, and a curve (to be referred to as “vibration leveldistribution” hereinafter) indicative of a vibration level distributionshowing vibration detection positions on the time axis of the abovewaveform as shown in FIG. 3 is drawn by the vibration distributioncomputing means 14. A power value of vibration level was used as thesize of the above vibration level.

[0103] Vibration is generated in the leading edge portion (1) before thetread by an impact when the tread 1 contacts the road surface L. In thetread (ground contact portion) (2) where the tread 1 contacts the roadsurface L, as the tread 1 is confined to the road surface L, vibrationis rarely generated. Thereafter, in the trailing edge portion (3),vibration is generated again by releasing the above confinement as soonas the tread 1 departs from the road surface L.

[0104] The positions of the above leading edge portion (1), groundcontact portion (2) and trailing edge portion (3) and the vehicle speedV are detected by the vehicle speed detection means 12 based on theoutput pulse of the revolution sensor 12 a mounted to each unshownwheel.

[0105] The vibration level of the above tread 1 depends mainly on thecondition of a road surface on which the vehicle is running and vehiclespeed.

[0106]FIG. 4(a) is a diagram showing the vibration level distribution ofthe tread 1 when a test vehicle runs on a regular dry asphalt road at alow speed (V=20 km/h) and FIG. 4(b) is a diagram showing the vibrationlevel distribution of the tread 1 when the test vehicle runs at a highspeed (V=90 km/h).

[0107] Meanwhile, when the road surface friction coefficient μ is low,which is generally considered as dangerous, the vibration leveldistribution of the tread 1 greatly differs from that when the vehicleruns on the above dry asphalt road. For example, even when the vehicleruns on an iced road which is considered to have an extremely low roadsurface friction coefficient μ at a low speed (V=20 km/h), as constraintfrom the ground contact surface is small, the tread 1 greatly vibratesin the ground contact portion (2) where vibration is rarely generated asshown in FIG. 5(a). When the vehicle runs on a thick water film at ahigh speed (V=90 km/h), a hydroplaning phenomenon occurs and thevibration level of the tread 1 further increases in the ground contactportion (2) and the tread 1 greatly vibrates even in the leading edgeportion (1) as shown in FIG. 5(b).

[0108] This is because the tread 1 greatly vibrates even in the groundcontact portion (2) where vibration is rarely generated as constraintfrom the ground contact surface is small when the road surface frictioncoefficient μ is low or when the tire is floated by the water film.Particularly when a hydroplaning phenomenon occurs, the vibration of thetread 1 occurs at a position before the essential ground contact surfaceby a water film or water stream formed in front of the tire.

[0109] In this Embodiment 1, the vehicle comprising the vibration sensor11 mounted on the inner surface 1A of the tread 1 is caused to run onroads which differ in road surface friction coefficient μ at a speed Vto obtain the vibration level distribution of the tread 1 from thecondition of a road surface and the vehicle speed V as parameters, andthis vibration level distribution is stored in the vibration levelstorage means 16 of the vehicle running state estimation apparatus 10 asa master curve for estimating the condition of a road surface.

[0110] Therefore, the vibration level distribution of the tread 1obtained by the vibration level distribution computing means 14 and theabove master curve stored in the above vibration level storage means 16are compared with each other to estimate the condition of a roadsurface.

[0111] Alternatively, the operation of comparing the measured vibrationdistribution curve and the master curve is simplified, a threshold valueis set for one or a plurality of predetermined vibration levels atdetection positions or for a predetermined time range, and the road isestimated as a low-μ road when the above computed vibration levelexceeds the above threshold value. For example, the vibration level ofthe tread 1 in the ground contact portion (2) which satisfiesrequirements for road surface friction coefficient μ and vehicle speedwhich are considered as safe is stored in the vibration level storagemeans 16 as the above threshold value and the computed vibration levelof the tread 1 in the ground contact portion (2) while running iscompared with the above threshold value to estimate whether the road onwhich the vehicle is running is a safe high-μ road or slippery low-μroad. It may estimated whether the road is a high-μ road or low-μ roadfrom the two vibration levels of the leading edge portion (1) and theground contact portion (2).

[0112] Alternatively, the ratio (P1:P2:P3) of the power values ofvibration level at the positions (1), (2) and (3) under variousconditions of a road surface such as a regular dry road and an iced roadis stored for each speed and compared with the ratio of the power valuesof vibration level at the positions (1), (2) and (3) in the computedvibration level distribution to estimate the condition of a roadsurface.

EMBODIMENT 2

[0113] In the above Embodiment 1, the vibration levels of a portionbelow the spring of the vehicle measured by the vibration sensor 11 arearranged in time sequence by the vibration waveform detection means 13and the vibration level distribution of the tread 1 is obtained by thevibration level distribution computing means 14 to estimate thecondition of a road surface. As shown in FIG. 6, frequency analyzingmeans 14F for obtaining the frequency spectrum of vibration levelobtained by converting the frequency of the above vibration level andvibration level calculating means 14S for calculating a vibration levelat a predetermined frequency band of the obtained frequency spectrum areprovided in place of the above vibration level distribution computingmeans 14, and further road surface condition estimation means 15S forestimating the condition of a road surface by comparing the vibrationlevel calculated by the above vibration level calculating means 14S witha master curve for estimating the condition of a road surface from thefrequency spectrum of vibration level stored in the vibration levelstorage means 16S is provided to estimate the condition of a roadsurface from the vibration level at a predetermined frequency band ofvibration of a portion below the spring of the vehicle.

[0114] FIGS. 7(a) and 7(b) show the vibration spectra of the tread 1when the vehicle ran on a regular dry asphalt road and the road surfacefriction coefficient μ was considered to be extremely low. FIG. 7(a)shows the spectrum of vibration when the vehicle ran on an iced road ata low speed (V=20 km/h) and FIG. 7(b) shows the spectrum of vibrationwhen the vehicle ran on a water film at a high speed (V=90 km/h).

[0115] When the frequency components of the above vibration spectra wereanalyzed, it was found that the vibration level at a frequency of 500 Hzto 2 kHz greatly changes according to the condition of a road surface.This frequency component is identical to the frequency component ofvibration right after the tread 1 departs from the tread on a regularroad surface and estimated to be caused by the shear or the naturalfrequency of distortion of a tread block. Then, it is possible toestimate the condition of a road surface by comparing the vibrationlevel at a frequency of about 1.4 kHz which is the natural frequency ofthe tread block in the above frequency spectrum.

[0116] Therefore, the condition of a road surface can be estimated byobtaining the frequency spectrum of vibration level obtained in the sameactual vehicle test as in the above Embodiment 1, storing this vibrationspectrum as a master curve for estimating the condition of a roadsurface, frequency converting the vibration waveform of the tread 1obtained by the vibration waveform detection means 13 by means of thefrequency analyzing means 14F, and comparing the vibration level at apredetermined frequency range obtained by the vibration levelcalculating means 14S with the above master curve stored in thevibration level storage means 16S.

[0117] Further, the operation of comparing the measured frequencyspectrum with the master curve of the above frequency spectrum issimplified, a vibration level at one or more frequencies close to thefrequency of natural vibration of the above tread land portion (block)or a predetermined frequency band is calculated, a threshold value isset for the above vibration level, and it is estimated that the road isa low-μ road when the above vibration level exceeds the above thresholdvalue.

EMBODIMENT 3

[0118] In the above Embodiment 2, the condition of a road surface isestimated from the vibration level at a predetermined frequency bandcalculated by the vibration level calculating means 14S. As shown inFIG. 8, vibration level computing means 14 for computing at least twovibration levels at different frequency bands of the obtained frequencyspectrum is provided in place of the above vibration level calculatingmeans 14 s, and road surface condition estimation means 15S forestimating the condition of a road surface by comparing the computedvalue of vibration level computed by the above vibration level computingmeans 14R with a master curve for estimating the condition of a roadsurface from the frequency spectrum of vibration level stored in thevibration level storage means 16R is provided to estimate the conditionof a road surface.

[0119] The above two frequency bands are preferably 300 to 1,000 Hzwhich is hardly affected by the condition of a road surface and 800 to5,000 Hz which reflects the slipperiness of a road surface in thespectrum of vibration of a portion below the spring of the vehicle shownin FIGS. 7(a) and 7(b).

[0120] The computed value of vibration level is not limited to a valueat the above two frequency bands and a computed value of vibration levelat three or more frequency bands may be computed to estimate thecondition of a road surface.

[0121]FIG. 9 shows the results of computing the ratio α of the averagevalue of vibration level at a frequency band of 300 to 1,000 Hz to theaverage value of vibration level at a frequency band of 1,000 to 2,000Hz when the vehicle runs on a dry road, wet road and iced road at avehicle speed of 15 to 90 km/h.

[0122] On the dry road, the above computed value α is about 0.4 with newtires and worn-away tires regardless of the speed whereas on the wetroad, the above computed value α becomes larger as the vehicle speedincreases and worn-away tires than new tires. This is because ahydroplaning phenomenon occurs that the vehicle is in a slipperydangerous state when the vehicle runs on the wet road at a high speedwith worn-away tires. Meanwhile, on the iced road, the above computedvalue α is large at 0.8 to 1.1 regardless of the vehicle speed.

[0123] Thus, by using a computed value from a vibration level at aplurality of frequency bands, the risk of the condition of a roadsurface can be judged accurately on a real-time basis regardless of thespeed and the abrasion of the tire.

[0124] At this point, the reference value which is a threshold value isset using the relationship between the road surface friction coefficientμ and the above computed value α to judge the condition of a roadsurface (1) as normal when α is equal to or smaller than 0.6, (2) asrequiring care when α is larger than 0.6 and equal to or smaller than0.9 and (3) as dangerous when α is larger than 0.9 (hydroplaning, snowroad or iced road). Thus, the slipperiness=risk of the road surface onwhich the can is running can be judged.

EXAMPLE

[0125] The following test was conducted using a vehicle with the vehiclerunning state estimation apparatus 10 of the present invention and analarm device which gives an alarm that care must be taken to the driverwhen the above computed value α obtained by the vibration levelcomputing means 14R exceeds 0.6 and an alarm for a danger when the valuea exceeds 0.9.

[0126] On a dry road and a wet road having a water depth of 10 mm, thevehicle ran with new tires and worn-away tires at a speed of 30 to 90km/h and on an iced road, the vehicle ran with new tires at a speed of15 to 60 km/h.

[0127] As a result, on the wet road, an alarm that care must be takenwas given when the vehicle ran at a speed of 60 km/h or more with newtires and at a speed of 45 km/h or more with worn-away tires and analarm for a danger was given when the vehicle ran at a speed of 90 km/hor more with new tires and at a speed of 70 km/h or more with worn-awaytires. When the vehicle ran with new tires on the iced road, an alarmthat care must be taken was given at a speed of 15 km/h or more and analarm for a danger was given at a speed of 30 km/h or more.

EMBODIMENT 4

[0128] In the above Embodiments 1 to 3, the method of estimating thecondition of a road surface by detecting the vibration level of aportion below the spring of a vehicle while running has been described.It is also possible to estimate the condition of a road surface fromvibration transmission characteristics between two pints of a portionbelow the spring of the vehicle by detecting the vibration states of thetwo points.

[0129]FIG. 10 is a block diagram showing the constitution of a vehiclerunning state estimation apparatus 20 according to Embodiment 4. In thefigure, reference symbols 21A and 21B denote first and second vibrationsensors mounted at two different points of a portion below the spring ofthe vehicle, 12 vehicle speed detecting means comprising a revolutionsensor 12 a, 23 transmission function computing means for computing avibration transmission function between the above two points from theoutput levels (vibration levels) of the above first and second vibrationsensors 21A and 21B, 24 vibration transmission level computing means forcomputing a vibration level at a predetermined frequency band from thefrequency characteristics of the above transmission function, and 25road surface condition estimating means for receiving the above computedvibration transmission level and a vehicle speed from the above vehiclespeed detecting means 12 and estimating the running state of the vehicleby estimating the condition of a road surface from the above computedvibration transmission level using the previously obtained G-μ mapshowing the relationship between the vibration transmission level foreach vehicle speed and the condition of a road surface, stored in thevibration level storage means 26.

[0130] The two points which differ from each other in relative vibrationcharacteristics and are required for obtaining vibration transmissioncharacteristics are preferably two points sandwiching a buffer member.Therefore, in this Embodiment 4, as shown in FIG. 11, the abovevibration sensors 21A and 21 b are mounted on the outer side of the rim2A of a tire wheel portion 2 and on the suspension arm 3A of asuspension 3. The suspension arm 3A on which the above vibration sensor21B is mounted is connected to a hub portion 3C through a proximalrubber bush 3B, whereby the two vibration sensors 21A and 21B arearranged with the buffer member therebetween.

[0131] FIGS. 12(a) and 12(b) show the measurement results of vibrationtransmission levels measured by the first and second vibration sensors21A and 21B mounted on the tire wheel portion 2 and the suspensionportion 3 which are portions below the spring of the vehicle,respectively. FIG. 12(a) shows the vibration transmission levels at alow speed (V=20 km/h) and FIG. 12(b) shows the vibration transmissionlevels at a high speed (V=90 km/h).

[0132] As obvious from the figures, the vibration transmission levels onan iced road and a water film are extremely higher at a frequency bandof 500 Hz to 2 kHz than the vibration transmission levels on a regulardry asphalt road. This is because the wheel including the tire isexcited by the vibration within the tread of the tread 1, and vibrationbetween the tire and the wheel and between the suspension and the wheelis easily transmitted as constraint from the road surface of the tread 1is small due to a low-μ road, resulting in an increase in vibrationtransmission level at the above frequency band.

[0133] Therefore, by monitoring the vibration transmission level at theabove band, the condition of a road surface can be estimated. Statedmore specifically, the frequency spectra of vibration transmissionlevels on various road surface conditions are previously obtained andstored as a master curve for estimating the condition of a road surface,a vibration transmission function obtained by the transmission functioncomputing means 23 is frequency converted, and the obtained frequencyspectrum is compared with the above master curve of the frequencyspectra to estimate the condition of a road surface. Alternatively, thevibration transmission level at a frequency band of 500 Hz to 2 kHz iscalculated, a threshold value is set for the above vibrationtransmission level and it is estimated that the road is a low-μ roadwhen the above vibration transmission level exceeds the above thresholdvalue.

[0134] In this Embodiment 4, unlike the prior art described in the aboveJapanese Laid-open Patent Application No. 11-94661, the vibrationtransmission level between two points of the portion below the spring ofthe vehicle is monitored, thereby making it possible to estimate thecondition of a road surface with high accuracy without being influencedby disturbance such as the roughness of the road surface.

[0135] As shown in FIG. 13, a metal “float” 4 may be mounted to the tirewheel portion 3 through a buffer member 5 made from an elastic materialand the second vibration sensor 21B may be mounted on this “float” 4 tomeasure vibration transmission characteristics between the above tirewheel portion 3 and the above “float” 4 with the first vibration sensor21A and the above second vibration sensor 21B mounted on the above tirewheel portion 3, respectively.

[0136] The buffer member 5 may be a stabilizer or a link bush or may bebonded to a portion below the existing spring. The buffer member is madefrom rubber having elastic characteristics (silicon-, olefin- orphenylene-based) or resin (urethane- or Teflon-based).

[0137] In the above Embodiments 1 to 4, the regular dry asphalt road andthe road having a low road surface friction coefficient μ have beentaken as examples of the road. The type of the road is not limited tothese and a road is suitably set according to the district andenvironment where the vehicle is used and the conditions of the roadsurface may be classified into three or more estimated conditions of theroad surface, for example, (1) high-μ road (μ≧0.6), (2) intermediate-μroad (0.3≦μ<0.6), and (3) low-μ road (μ<0.3).

[0138] Since the vibration level of the above Embodiments 1 to 3 and thevibration transmission level of the above Embodiment 4 are changed bytimes variations in the air pressure and temperature of each tire,rubber hardness or the abrasion amount of the tread. If the above mastercurve or the threshold value might be changeable by the above datavalues, the estimation accuracy of the condition of a road surface couldbe further improved.

[0139] In the above Embodiments 1 to 4, the condition of a road surfaceis estimated from the vibration level or vibration transmission levelusing the master curve of vibration waveforms or frequency spectra ofvarious road surface conditions. A running test and a braking test areconducted on various road surface conditions, vibration levels orvibration transmission levels at those times are measured, and the roadsurface friction coefficient μ between the tire and the test roadsurface is calculated from a braking distance on the road surface todraw a master curve of vibration waveforms or frequency spectra at eachroad surface friction coefficient μ, thereby making it possible toconstruct a road surface condition estimation apparatus capable ofestimating the road surface friction coefficient μ using the abovemaster curve from the vibration level or vibration transmission levelmeasured while running.

[0140] For example, FIG. 14 plots the road surface friction coefficientμ obtained from the braking distance on an iced road, snow road and dryasphalt road on the axis of abscissas and the size of vibrationtransmission level at 50 Hz to 2 kHz of the vibration transmissionfunction described in the above Embodiment 4 (at the time of running ata fixed speed of 20 km/h) on the axis of ordinates. Thus, since theabove road surface friction coefficient μ and the vibration transmissionlevel are closely correlative to each other (R²=0.9983), the roadsurface friction coefficient μ can be estimated from the vibrationtransmission level measured while running with high accuracy.

EMBODIMENT 5

[0141] In the above Embodiments 1 to 4, the method of estimating thecondition of a road surface from the vibration level or vibrationtransmission level of a portion below the spring of the vehicle has beendescribed. When it is estimated from the above vibration level orvibration transmission level how slippery the surface of the road is andthe condition of the road surface is estimated to be slippery, it ispossible to warn the driver or passenger of the risk.

[0142]FIG. 15 is a diagram showing the constitution of a roadslipperiness warning apparatus 30 according to Embodiment 5. The roadslipperiness warning apparatus 30 comprises map storage means 36 forstoring a warning zone map having two warning zones Z1 and Z2 surroundedby vehicle speed V and the size of vibration level shown in FIG. 16 inplace of the vibration level storage means 16 of the above Embodiment 1,road condition judging means 35 for judging where the vibration level ofthe tread 1 obtained by the vibration distribution computing means 14and vehicle speed are positioned in the above warning zone map in placeof the road surface condition estimation means 15 of the aboveEmbodiment 1, and further warning means 37 for warning the driver orpassenger of a risk when the measured vibration level and vehicle speedare in the above warning zone Z1 or Z2.

[0143] The road slipperiness warning apparatus 30 of Embodiment 5activates the warning means 37, for example, turns on and off an unshownred lamp when the vibration level corresponding to the vehicle speed ofthe tread 1 is in the warning zone Z1 of the first stage and sounds analarm and turns on and off the above red lamp when the above vibrationlevel is in the warning zone Z2 of the second stage. Thus, the roadslipperiness warning apparatus 30 warns the driver or passenger of therisk of the road surface. Since the risk of the condition of the roadsurface can be thereby informed of the driver while running, the drivercan take early operation to decelerate and a reduction in the number ofaccidents can be expected.

EXAMPLE

[0144] When a test vehicle with the above road slipperiness warningapparatus 30 was caused to run on a dry asphalt road or wet road (waterpool having a depth of 10 mm) by increasing the vehicle speed to 20, 40,60, 80 and 90 km/h gradually, the vibration level of the tread 1 rose asthe vehicle speed increased on the regular dry asphalt road (marked with) and the wet road (marked with O) where hydroplaning easily occurs asshown in FIG. 16. Particularly when the road was wet and the vehiclespeed was high, the above vibration level jumped up. On the wet road,the warning of the first stage was given when the vehicle speed became60 km/h and the warning of the second stage was given when the vehiclespeed became 80 km/h or more. Thus, it was confirmed that the object ofthe present invention could be attained.

[0145] In the above Embodiment 5, a warning was given by estimating theslipperiness of the road by obtaining the vibration level distributionof a portion below the spring of the vehicle measured by the vibrationsensor like the above Embodiment 1. Like the above Embodiments 2 and 3,the slipperiness of the road may be estimated from the vibration levelat a predetermined frequency band or the value obtained by carrying outan operation on at least two vibration levels at different frequencybands of the frequency spectrum of vibration level obtained by frequencyconverting the above vibration level.

EMBODIMENT 6

[0146] In the above Embodiment 5, the risk of the road condition isdirectly judged from the measured vibration level of the portion belowthe spring of the vehicle. The vibration states of two points of theportion below the spring of the vehicle are detected and theslipperiness of the road surface is estimated from the vibrationtransmission level between the above two points to give a warning.

[0147]FIG. 17 is a diagram showing the constitution of a roadslipperiness warning apparatus 40 according to Embodiment 6 of thepresent invention. The road slipperiness warning apparatus 40 comprisesmap storage means 46 for storing a warning zone map having two warningzones K1 and K2 surrounded by the vehicle speed V and the vibrationtransmission level G shown in FIG. 18 in place of the vibration levelstorage means 26 of the above Embodiment 4, road surface conditionjudging means 45 for judging where the vibration transmission levelobtained by the vibration transmission level computing means 24 andvehicle speed are located in the above warning zone map in place of theroad surface condition estimation means 25, and further warning means 47for warning the driver or passenger of a risk when the above measuredvibration transmission level and vehicle speed are in the above warningzone K1 or K2. When the vibration level of the tread and the vehiclespeed are in the warning zone K1 of the first stage or the warning zoneK2 of the second stage, the warning means 47 is activated to warn thedriver or passenger of the risk of the road surface.

EXAMPLE

[0148] When a test vehicle with the above road slipperiness warningapparatus 40 was caused to run on a dry asphalt road and a frozen roadat a fixed speed of 20, 30 or 40 km/h, a warning of the second stage wasgiven at all the speeds on the frozen road. Thus, it was confirmed thatthe object of the present invention could be attained.

[0149] In the above Embodiments 5 and 6, the risk of the road surfacecondition is directly judged from the measured vibration transmissionlevel. An estimated road surface condition computing apparatus similarto the vehicle running state estimation apparatuses 10 and 20 of theabove Embodiments 1 to 4 may be constructed and a risk may be warned tothe driver or passenger according to the condition of a road surfacecomputed by the estimated road surface condition computing apparatus. Inthis case, it is needless to say that the above road surface conditionsand the warning zones must be set to relate the estimated road surfaceconditions with the set warning zones.

EMBODIMENT 7

[0150] In the above Embodiment 2, the method of estimating the conditionof a road surface by calculating a vibration level at a predeterminedfrequency band from the frequency spectrum of the vibration level of aportion below the spring of the vehicle obtained by the frequencyanalyzing means 14F has been described. As shown in FIG. 19, tirenatural vibration calculating means 17A for calculating the frequency ofnatural vibration of each tire from a vibration level at a frequencyband of 200 Hz or less of the detected vibration level, tire airpressure estimation means 17B for estimating the air pressure of eachtire from the calculated frequency of natural vibration of the tire andtire running state estimation means 18 for estimating the running stateof each tire from the estimated air pressure of the tire are provided toestimate the running state of the tire which is one of the runningstates of the vehicle.

[0151]FIG. 20 shows the relationship between the frequency of naturalvibration of the tire (Hz) and the air pressure (MPa) of the actualtire. Since the above frequency of natural vibration of the tire and theair pressure of the tire are closely correlative to each other(R²=0.9891), the vibration level of a portion below the spring of thevehicle is detected and frequency analyzed so that the air pressure ofthe tire can be estimated from a vibration level at a frequency band of200 Hz or less of the detected vibration level with high accuracy.

[0152] In this embodiment, tire pressure monitoring means 19A formonitoring the pressure of the tire while running using the aboveestimated air pressure and tire pressure reduction warning means 19B forwarning the passenger of a reduction in the pressure of the tire whenthe air pressure monitored by the above tire pressure monitoring means19A falls below a predetermined value are provided to warn the passengerof a reduction in the pressure of the tire. Thereby, the running stateof the tire can be estimated and when the pressure of the tire monitoredwhile running falls below a predetermined value, this can be warned tothe passenger, thereby making it possible to improve the safety of thevehicle.

EMBODIMENT 8

[0153] In the above Embodiment 7, the air pressure of the tire isestimated by calculating the frequency of natural vibration of the tirefrom a vibration level at a frequency band of 200 Hz or less of thevibration level of a portion below the spring of the vehicle by means ofthe tire natural vibration calculating means 17A and the tire airpressure estimation means 17. As shown in FIG. 21, tire revolution speeddetection means 27, tire running state estimation means 28 forestimating the state of the tire while running by calculating theaverage value of vibration level changing by the revolution speed of thetire at a frequency band of 100 Hz or less of the detected vibrationlevel, tire abnormality detection means 29A for judging that the tire isabnormal when the calculated average value of vibration level exceedsthe preset reference value and tire abnormality warning means 29B forwarning the passenger of the abnormality of the tire based on thedetection result of the above tire abnormality detection means 29A areprovided to estimate the running state of the tire and to judge theabnormality of the tire, thereby making it possible to warn thepassenger of this abnormality.

[0154] For example, when part of the tread portion peels off, air in theinside of the tire is excited by the generation of vibration each timethe part contacts the surface of a road. As the initial peel-off troubleoccurs at one site on the outer surface of the tire, vibration generatedthereby is periodical according to the revolution of the tire. The cycleis about 14 Hz (primary), 28 Hz (secondary) and 42 Hz (tertiary) at aspeed of 100 km/h in the case of a tire for a general passenger vehicle.The above peak generally appears by the ground contact of the tire evenwhile running but when a peel-off trouble occurs at one site on theouter surface of the tire, the above peak level is extremely high,whereby it is estimated that something abnormal occurs in the tire.

[0155] Therefore, a vibration level at a frequency band of 100 Hz orless (for example, 14 Hz, 28 Hz or 42 Hz) of the vibration level of aportion below the spring of the vehicle is calculated by the above tirerunning state estimation means 28, it is judged that the tire isabnormal condition when the average value of the calculated vibrationlevel exceeds a predetermined reference value, and this information issent to the tire abnormality detection means 29A to warn the occurrenceof abnormality in the tire to the passenger.

[0156]FIG. 22 is a diagram showing the result of comparison between thevibration level (dB) of a defective tire having a cut at one site on theouter surface between the tire tread and the steel belt and that of anormal tire. Stated more specifically, the above defective tire and thenormal tire were caused to run on an indoor drum at a fixed speed of 100km/h to measure their vibration levels and analyze the frequencies ofthe vibration levels.

[0157] As described above, even in the case of the normal tire, peaksappear at frequencies of about 14 Hz (primary), 28 Hz (secondary), 42kHz (tertiary), whereas in the case of the defective tire, as shown by abroken line in the figure, the sizes of the peaks are about 20 dB largerthan those of the normal tire. The peaks are much higher than the peaksof the normal tire at the above frequencies, which are set as referencesfor detecting a tire trouble and a tire trouble can be detected bydetecting the vibration level of the portion below the spring of thevehicle.

[0158] The above reference value is set to a range of 1.2 to 5 times thevibration level at a reference decision frequency Fn=n×V/(2πr) when thevehicle runs at a predetermined vehicle speed V while no abnormalityoccurs in the tire to detect the above abnormality with high accuracy.In the above equation, r is the rolling radius of the tire and n is anatural number.

[0159] The above reference value can be changed by time variations intemperature, the abrasion amount of the tire tread or the deteriorationof the hardness of rubber.

EMBODIMENT 9

[0160]FIG. 23 is a diagram showing the constitution of a vehicle controlapparatus 50 according to Embodiment 9. The vehicle control apparatus 50comprises vibration sensors 21A and 21B installed at two differentpoints of a portion below the spring of the vehicle, vehicle detectionmeans 12, transmission function computing means 23 for computing avibration transmission function between the above two points from theoutput levels (vibration levels) of the above vibration sensors 21A and21B, vibration transmission level computing means 24 for computing avibration level at a predetermined frequency band from the frequencycharacteristics of the above transmission function, road surfacecondition estimation means 25 for receiving the above computed vibrationtransmission level and a vehicle speed from the above vehicle speeddetection means 12 and estimating the condition of a road surface usingthe previously obtained G-μ map showing the relationship betweenvibration transmission level for each vehicle speed and the condition ofa road surface stored in the vibration level storage means 26, andvehicle control means 57 for controlling the running state of thevehicle based on the estimated condition of the road surface obtained bythe road surface condition estimation means 25.

[0161] The above vehicle control apparatus 57 controls the air pressureof the tire based on the above estimated condition of the road surfaceand shortens the braking distance on a slippery road. For example, byreducing the air pressure of the tire on a low-μ road such as an icedroad, the braking distance on the low-μ road can be shortened.

[0162] That is, when the road is estimated as a low-μ road, the airpressure of the tire is automatically or manually reduced by the vehiclecontrol means 57 to increase the ground contact area of the tire,thereby increasing friction force between the road surface and the tireto shorten the braking distance.

[0163] Any tire air pressure automatic control system is acceptable butthe system comprises a pressure meter, controller, wheel with a pressurecontrol valve, flexible joint hose, spare tank and compressor, forexample.

[0164] The vehicle control apparatus 50 may be provided with means ofwarning the driver or passenger of a risk according to the condition ofthe road surface as described above to control the running state andgive a warning at the same time.

EXAMPLE

[0165] A braking test was conducted on a dry asphalt road and an icedroad using a test vehicle which was loaded with the vehicle controlapparatus 50 of this Embodiment 9 to control the air pressure of eachtire in order to confirm whether the braking distance could be shortenedby controlling the air pressure of the tire automatically when thevehicle was braked on the frozen road. The above vehicle controlapparatus 50 was provided with a road slipperiness warning apparatussimilar to those of above Embodiments 5 and 6.

[0166] It was first confirmed that when the test vehicle of the presentinvention was caused to enter a frozen road at a fixed speed V of 20km/h, a warning was given and at the same time the air pressure of thetire was automatically reduced from 220 to 160 kPa. This is because whenit is detected that the vehicle enters the frozen road, the computer isprogrammed to give an instruction to reduce the air pressure. Further,when a braking test was conducted on a dry asphalt road and a frozenroad, the braking distance of a vehicle with a conventional controlapparatus was 85% longer than when running on the asphalt road whereasthe braking distance of the test vehicle of the present invention was59% longer. That is, the braking distance of the present invention canbe shortened by about 14% on the asphalt road and about 30% on thefrozen road. It was confirmed from this result that the vehicle can stopsafely even on a frozen road by using the vehicle control apparatus 50of this Embodiment 9.

[0167] In the above Embodiment 9, vehicle control means for controllingthe locked state of each wheel and the air pressure of each tire basedon the estimated condition of a road surface is provided to control thebraking distance on a low-μ road. The braking distance on a low-μ roadcan also be shortened by performing the attitude control of a vehicle bycontrolling the brake unit of each wheel independently.

[0168] Alternatively, vehicle control means for controlling the attitudeof a vehicle may be provided to carry out the attitude control of thevehicle, for example, by controlling the brake unit of each wheelindependently based on the estimated condition of a road surface,thereby making it possible to reduce the braking distance on a low-μroad.

[0169] Further, vehicle control means for controlling the idling stateof each wheel may be provided to control the idling state of the wheelby controlling the brake unit or engine speed based on the estimatedcondition of a road surface, thereby making it possible to reduce thebraking distance on a low-μ road.

[0170] Further, in a vehicle with an automatic driving system, vehiclecontrol means for controlling to change the inter-vehicle distance setvalue may be provided to change the above inter-vehicle distance setvalue based on the estimated condition of a road surface so as tocontrol the inter-vehicle distance to an appropriate value, therebymaking it possible to keep a safe inter-vehicle distance even on a low-μroad without fail.

[0171] In the above example, the running state of a vehicle iscontrolled based on the condition of a road surface estimated from avibration transmission level like Embodiment 4. Like Embodiments 1 to 3,the running state of a vehicle may be controlled based on the conditionof a road surface estimated from a vibration level.

[0172] Alternatively, the running state of a vehicle may be controlledbased on the running state of each tire estimated by the tire runningstate estimation means 18 or 28 shown in Embodiment 6 or 7.

[0173] As having been described above, according to the presentinvention, the vibration level of the portion below the spring of arunning vehicle or the vibration transmission level between at least twopoints of the portion below the spring of a vehicle is detected toestimate the condition of a road surface on which the vehicle isrunning. Therefore, even when the road is rough, which has beendifficult with the prior art, or when the slip angle is null, thecondition of the road surface can be estimated accurately. Using theestimated condition of the road surface, the risk of the condition ofthe road surface is warned to the passengers or the feedback control ofthe running state of the vehicle can be performed, thereby making itpossible to greatly improve the safety of the vehicle.

[0174] Further, the condition of a road surface or the air pressure ofeach tire is detected from a vibration level at a plurality of frequencybands of the vibration level to detect the condition of the road surfaceor the running state of the tire including the existence of abnormalityof the tire. Therefore, a multi-function sensing system which canaccurately detect the condition of a road surface, tire pressure andfurther the existence of tire abnormality with one sensor, has a simplestructure and many functions and is inexpensive can be constructed.

[0175] In the present invention, since an apparatus for estimating theground contact condition of each tire or the condition of a road surfaceand a power generating unit for generating power by the rolling of thetire and supplying power to the above apparatus are mounted to a tirewheel to control the characteristics of each tire based on the estimatedrunning state of the vehicle, the ground contact state of the tire canbe estimated and controlled stably for a long time without changing thestructure of the vehicle body.

[0176] Further, since the above power generating unit comprises a rotormagnetized and rotated by the rolling of the tire, a stator made from ahigh magnetic permeability material and adjacent to the rotor, a powergenerating coil installed within a magnetic circuit including the aboverotor and stator and a capacitor for accumulating electromotive forcegenerated in this power generating coil, power supply is made possibleby energy obtained from the rolling of the tire semi-permanently and itsfunctions can be retained stably for a long time.

What is claimed is:
 1. A vehicle running state estimation methodcomprising the steps of: detecting the vibration level of a portionbelow the spring of a running vehicle; and estimating at least one ofthe condition of a road surface on which the vehicle is running and therunning state of each tire based on the detected vibration level toestimate the running state of the vehicle.
 2. The vehicle running stateestimation method according to claim 1, wherein the waveform of timechanges in the vibration level is detected and the condition of a roadsurface on which the vehicle is running is estimated from a vibrationlevel at a predetermined position of this waveform or for apredetermined time range.
 3. The vehicle running state estimation methodaccording to claim 1, wherein the frequency of the detected vibrationlevel is analyzed to calculate a vibration level at a predeterminedfrequency band and the condition of a road surface on which the vehicleis running is estimated from the calculated vibration level.
 4. Thevehicle running state estimation method according to claim 1, whereinthe frequency of the above detected vibration level is analyzed, atleast two vibration levels at different frequency bands are calculated,an operation is carried out on the above calculated vibration levels,and the condition of a road surface on which the vehicle is running isestimated from the computed value.
 5. The vehicle running stateestimation method according to claim 1, wherein the vibration levels ofat least two points of a portion below the spring of a running vehicleare detected to calculate the vibration transmission level of theportion below the spring of the vehicle, and the condition of a roadsurface on which the vehicle is running is estimated from the calculatedvibration transmission level.
 6. A vehicle running state estimationapparatus comprising: means of detecting the vibration level of aportion below the spring of a running vehicle; means of computing thewaveform of time changes in the vibration level; and road surfacecondition estimation means for estimating the condition of a roadsurface on which the vehicle is running from a vibration level at apredetermined position of the waveform or for a predetermined timerange.
 7. The vehicle running state estimation apparatus according toclaim 6 which further comprises means of calculating the vibration levelof at least one of a tire leading edge portion, tire ground contactportion and tire trailing edge portion of the waveform.
 8. A vehiclerunning state estimation apparatus comprising: means of detecting thevibration level of a portion below the spring of a running vehicle;means of calculating a vibration level at a predetermined frequency bandby analyzing the frequency of the detected vibration level; and roadsurface condition estimation means for estimating the condition of aroad surface on which the vehicle is running from the calculatedvibration level.
 9. A vehicle running state estimation apparatuscomprising: means of detecting the vibration level of a portion belowthe spring of a running vehicle; and road surface condition estimationmeans for estimating the condition of a road surface on which thevehicle is running from a value obtained by carrying out an operation onat least two vibration levels at different frequency bands by analyzingthe frequency of the above detected vibration level.
 10. A vehiclerunning state estimation apparatus comprising: means of detecting thevibration levels of at least two points of a portion below the spring ofa running vehicle; means of calculating a vibration transmission levelat a predetermined frequency band between the at least two of thevibration detection points; and road surface condition estimation meansfor estimating the condition of a road surface on which the vehicle isrunning from the calculated vibration transmission level.
 11. Thevehicle running state estimation apparatus according to claim 10,wherein a vibration buffer member is interposed between the at least twovibration detection points.
 12. The vehicle running state estimationapparatus according to any one of claims 8 to 11, wherein therelationship between road surface friction coefficient μ obtained fromthe braking distances of a vehicle under various road conditions atdifferent speeds and the vibration level at a predetermined frequencyband, the computed value of vibration level or vibration transmissionlevel is obtained previously and the road surface friction coefficient μat the time of running is estimated based on the relationship.
 13. Thevehicle running state estimation apparatus according to any one ofclaims 8 to 12, wherein the frequency band is a band including thefrequency of natural vibration of a tire tread land portion.
 14. Thevehicle running state estimation apparatus according to any one ofclaims 8 to 13, wherein a threshold value is set for the vibration leveland the surface of a road is estimated to be in a low friction conditionwhen the calculated vibration level exceeds the threshold value.
 15. Thevehicle running state estimation apparatus according to claim 14,wherein the threshold value can be changed.
 16. The vehicle runningstate estimation apparatus according to any one of claims 6 to 15 whichfurther comprises vehicle speed detection means to estimate thecondition of a road surface based on vehicle speed.
 17. A vehiclerunning state estimation apparatus comprising the vehicle running stateestimation apparatus of any one of claims 6 to 16, means of judging theslipperiness of a road surface based on the condition of the roadsurface estimated by the road surface condition estimation means andwarning means for giving a warning when it is judged that the conditionof the road surface is slippery.
 18. The vehicle running stateestimation apparatus according to claim 17 which further comprisesvehicle speed detection means to change decision on the slipperiness ofa road surface and warning level based on vehicle speed.
 19. A vehiclerunning state estimation apparatus comprising: means of detecting thevibration level of a portion below the spring of a running vehicle;means of estimating the air pressure of each tire by calculating thefrequency of natural vibration of the tire from a vibration level at afrequency band of 200 Hz or less of the detected vibration level; andtire running state estimation means for estimating the condition of eachtire while running from the estimated air pressure of the tire.
 20. Thevehicle running state estimation apparatus according to claim 19 whichfurther comprises tire pressure monitoring means for monitoring thepressure of each tire while running using the estimated air pressure ofthe tire.
 21. The vehicle running state estimation apparatus accordingto claim 20 which further comprises warning means for warning apassenger of a reduction in the pressure of the tire when the airpressure monitored by the tire pressure monitoring means falls below apredetermined value.
 22. A vehicle running state estimation apparatuscomprising: means of detecting the vibration level of a portion belowthe spring of a running vehicle; tire revolution speed detection means;tire running state estimation means for estimating the state of eachtire while running by calculating the average value of vibration levelchanging by the revolution speed of the tire at a frequency band of 100Hz or less of the detected vibration level; and tire trouble detectionmeans for judging that the tire is abnormal when the calculated averagevalue of vibration level exceeds a preset reference value.
 23. Thevehicle running state estimation apparatus according to claim 22,wherein the reference value is set to a range of 1.2 to 5 times thevibration level at a reference decision frequency Fn when the vehicleruns at a predetermined speed V while the tire is not abnormal:reference decision frequency Fn=n×V/(2πr) wherein r is the rollingradius of the tire, and n is 1, 2, 3, . . .
 24. The vehicle runningstate estimation apparatus according to claim 23, wherein the referencevalue can be changed.
 25. The vehicle running state estimation apparatusaccording to any one of claims 6 to 24 which further comprises atransmitter for transmitting the output of the vibration detection meansfor calculating a time change in vibration level or a vibration level ata predetermined frequency band.
 26. The vehicle running state estimationapparatus according to any one of claims 6 to 25 further comprising apower generating unit which is mounted to a tire wheel, generates powerby the rolling of each tire and supplies power for driving the vibrationdetection means or power for amplifying the output of the vibrationdetection means.
 27. A vehicle control apparatus comprising vehiclecontrol means for controlling the running state of a vehicle based onthe condition of a road surface estimated by the vehicle running stateestimation apparatus of any one of claims 6 to 26 and/or the runningstate of each tire.
 28. The vehicle control apparatus according to claim27 which comprises vehicle speed detection means to control the runningstate of a vehicle based on vehicle speed.
 29. The vehicle controlapparatus according to claim 27 or 28, wherein the vehicle control meanscontrols the locked state of each wheel.
 30. The vehicle controlapparatus according to claim 27 or 28, wherein the vehicle control meanscontrols the attitude of a vehicle.
 31. The vehicle control apparatusaccording to claim 27 or 28, wherein the vehicle control means controlsthe air pressure of each tire.
 32. The vehicle control apparatusaccording to claim 27 or 28, wherein the vehicle control means controlsthe idling state of each wheel.
 33. The vehicle control apparatusaccording to claim 27 or 28, wherein the vehicle control means changesthe inter-vehicle distance set value of an automatic driving system. 34.A tire wheel comprising the vehicle running state estimation apparatusfor estimating the running state of a vehicle by detecting the vibrationlevel of a portion below the spring of a running vehicle as set forth inclaims 6 to 26 and a power generating unit for generating power by therolling of each tire and supplying power to the vehicle running stateestimation apparatus.
 35. The tire wheel according to claim 34, whereinthe vehicle running state estimation apparatus is mounted to the tirewheel.
 36. The tire wheel according to claim 34 or 35, wherein the powergenerating unit comprises a rotor magnetized and rotated by the rollingof each tire, a stator made from a high magnetic permeability materialand adjacent to the rotor and a power generating coil installed within amagnetic circuit including the rotor and the stator.
 37. The tire wheelaccording to claim 36, wherein the power generating unit comprises meansof accumulating electromotive force generated in the power generatingcoil.
 38. The tire wheel according to claim 36 or 37, wherein the rotoris turned by rotating an unbalance weight the gravity center of therotary cone of which is eccentric to a rotary shaft by the rolling ofeach tire.
 39. The tire wheel according to claim 36 or 37, wherein anair stream generated by the rolling of each tire is introduced into thepower generating unit and the rotor is turned by the introduced airstream.